This invention relates generally to ovens and, more particularly, to a combination oven using both radiant and microwave energy.
In ovens including both radiant cooking elements and a magnetron, or microwave, cooking element, the cooking elements are controlled to provide reduced cooking time as compared to known radiant ovens, yet a wide variety of foods can be cooked in such ovens. One such combination oven is operable in a speed cooking mode wherein both radiant and microwave cooking elements are utilized, in a microwave only cooking mode wherein only the magnetron is utilized for cooking, and a radiant only cooking mode wherein only the lamps are utilized for cooking.
The radiant cooking elements, in one embodiment, are Halogen lamps. The power output from such lamps varies depending on the magnitude of the supply voltage. Specifically, with the Halogen lamps, the lamp resistance is constant and the output wattage is equal to input voltage squared over lamp resistance. Therefore, as the input voltage varies, the output wattage also varies.
In the United States, household voltages can vary by as much as ten percent. As a result, the output power of the heating components in a cooking appliance such as the above described combination oven can vary by more than twenty percent. Compensation for such variations must be provided in order to provide acceptable cooking results.
In an exemplary embodiment of the invention a time adjustment algorithm for a combination oven provides that total energy into the food is constant for an input voltage in a range between about 108 Volts and 132 Volts. More particularly, and in one embodiment, the time adjustment algorithm provides that total cooking time is adjusted by subtracting or adding a time adjustment value to a selected total cooking time. The time adjustment value, in one embodiment, is determined in accordance with the following relationship.
Time Adjustment=Total cooking time*{5(Voltage Deviation/120 Volts)2xe2x88x921.5(Voltage Deviation/120 Volts)}
The total cooking time value is determined in accordance with the power level selected by the user as described below in more detail. The voltage deviation value is the deviation from nominal 120 Volts. The time adjustment value may have a positive or negative value, and is simply added to the total cooking time value.
Using the above described time adjustment, the total energy into the food is maintained constant for input voltages in a range between about 108 Volts and 132 Volts. Such time adjustment provides that suitable cooking results are achieved even when the input voltage varies over a wide range.